The present invention relates to secondary lithium batteries. More particularly, the present invention relates to secondary or rechargeable lithium batteries using a lithium intercalation positive electrode (cathode) and a lithium intercalated negative electrode (anode).
Secondary lithium batteries using an intercalation compound as cathode and free lithium metal as anode were studied extensively during the 1980""s and 1990""s. These studies revealed the inherent dangers of using free lithium and precluded the commercial viability of such batteries. However, substitution of other intercalation compounds for the free lithium metal have proved to be successful.
These successful secondary lithium batteries have focused on the concept of a xe2x80x9crocking chair batteryxe2x80x9d, which utilize a lithiated intercalation compound as the cathode and a lithium intercalation compound as the anode. Upon charge of such a battery, the lithium deintercalates from the cathode and then intercalates with the anode. During discharge, the lithium flows in the opposite direction from anode to cathode. In other words, the lithium ions are xe2x80x9crockedxe2x80x9d back and forth during the charge-discharge cycle.
Because of loss of lithium associated with irreversible secondary reactions in these lithium batteries, an excess of lithium is necessary. This excess lithium may be provided by using an excess of cathode material, however, this results in a significant loss of battery capacity. Alternatively, a stable lithium based cathode containing more than one lithium atom per unit formula may be used.
Prior art cells utilized an LiCoO2 or an LiNiO2 cathode material, which have only one lithium ion per unit formula and therefore suffer from the loss of lithium noted above. There is no known Li,CoO2 phase in which x is greater than one. Further, the instability in air of Li1+xNiO2 prevents the use of this phase as the cathode material.
In light of the above deficiencies with respect to LiCoO2 and LiNiO2 cathode materials, U.S. Pat. No. 5,196,279 suggested use of lithium manganese oxide cathode materials and particularly, LiMn2O4 and Li2Mn2O4 cathode materials.
The use of Li2Mn2O4 as the cathode material is particular advantageous as it provides the excess lithium needed to overcome the loss caused by the irreversible reactions noted above. The ""279 patent relates solely to the use of a carbon anode which was the standard at the time and continues to be so. However, it is believed that in the next few years, carbon anodes will be replaced with inorganic electrode materials. These inorganic materials will have a large amount of irreversible lithium loss associated with their use as the anode material. Therefore, there is a need in the art to provide for excess lithium in secondary lithium batteries utilizing inorganic anode compounds.
In accordance with the present invention, secondary lithium batteries include a lithiated intercalation cathode compound and an inorganic compound for the negative electrode. The cathode compound comprises Li2Mn2xe2x88x92xMexO4xe2x88x92zFz wherein 0xe2x89xa6Xxe2x89xa60.5 and can be optimized to match the irreversible capacity loss associated with a chosen inorganic negative electrode and wherein 0xe2x89xa6Zxe2x89xa60.5 and wherein Me is selected from the group consisting of Al, Cr, Zn, Co, Ni, Li, Mg, Fe, Cu, Ti, Si or combinations thereof. In a preferred embodiment, the cathode compound comprises Li2Mn2O4.
The present invention further provides a rechargeable lithium battery comprising a positive electrode, a negative electrode, an electrically conductive collector associated with at least one electrode, a separator element arranged between the electrodes, wherein the positive electrode includes an intercalation compound of Li2Mn2xe2x88x92xMexO4xe2x88x92zFz as set forth above and the negative electrode includes an active inorganic compound.